The new strategy involves "supercooling" organs, to below
freezing temperatures, but without freezing them solid. In
experiments, this method significantly extended the amount of
time rat livers could be preserved for transplantation into donor
rats, to up to four days. (Normally, rat livers can only be
stored for up to about 24 hours before they become unusable, the
researchers said.)

More than 120,000 patients are waiting
to receive a donor organ in the United States today, and one
cause of this organ shortage lies in the limitations in how long
organs can be preserved — using current techniques, human organs
can be preserved for only about six to 12 hours before they decay
and become unusable.

However, the new supercooling technique could change that. "The
duration of preservation we have achieved — four days — is the
longest that has even been done that allows successful
transplantation," said study co-author Bote Bruinsma, a medical
engineer at Harvard Medical School in Boston. [ 9
Most Interesting Transplants ]

Extending the organ preservation time could allow donor organs to
be transplanted into people over a wider region, and give health
care teams more time to prepare organ recipients for transplant,
the researchers said.

Other methods of extending organ preservation time haven't been
practical, the researchers said. For instance, one method uses
machines
that constantly supply organs with fluid that, like
blood, is loaded with oxygen and can keep the organs alive.
However, keeping organs hooked up to machines for hours or days
is not practical for long-term organ preservation, the
researchers noted.

Another method is to keep organs as cold as possible to slow or
even stop the process of decay. However, cooling organs to
below-freezing temperatures can lead ice crystals to form within
the organs' cells, and can damage the tissues.

The new technique involves bringing organs to below-freezing
temperatures, but not freezing them solid. Instead, the
researchers infused them with
nontoxic antifreeze compounds that helped keep cells from
freezing even when they were 21.2 degrees Fahrenheit (minus 6
degrees C) — colder than the freezing temperature of water.

In addition, the researchers also used machine-circulated fluids
to nourish the organs and keep them alive. However, the
researchers did not have to keep the organs constantly suffused
with oxygenated fluid — rather, they needed machine perfusion
only for brief periods — one hour before supercooling and again
three hours after the livers were warmed back up to above
freezing temperatures.

All of the rats that received livers that were preserved for
three days survived at least three months after their
transplants, and nearly 60 percent of the rats that received
livers preserved for four days survived that long. In contrast,
none of the rat livers were viable when they were preserved for
three days using traditional methods.

"The fact that livers could be successfully transplanted at all
after being stored at subzero [Celsius] temperatures is a novel
finding," Bruinsma told Live Science. "The fact this work shows
that we can actually use this supercooling technique to markedly
extend preservation time is very exciting."

The researchers acknowledged that their new method is more
complicated than current preservation techniques. Still, they
"expect that the benefits will greatly outweigh the added
complexity," Bruinsma said.

This strategy could, in principle, be used for organs other than
the liver, such as kidneys, hearts and lungs, the researchers
said. "We expect only slight modification would be needed for
other organs," Bruinsma said, adding that portable fridges could
help keep organs supercooled during transport.

However, the investigators cautioned that further research is
needed to see if this technique could work with human organs.
"The most important difference is the size of the liver,"
Bruinsma said. Human livers are about 4.5 lbs. (about 2
kilograms), so they may be more challenging to supercool than rat
livers, which weigh 0.02 lbs. (10 grams).

"We are currently testing supercooling on human livers that were
discarded for transplantation and donated for research," Bruinsma
said. "This will allow us to test the feasibility of this
technique in the human organ."

The scientists detailed their findings online June 29 in the
journal Nature Medicine.